Multi-omics reveals the ecological and biological functions of Enterococcus mundtii in the intestine of lepidopteran insects.

Insect guts offer unique habitats for microbial colonization, with gut bacteria potentially offering numerous benefits to their hosts. Although Enterococcus has emerged as one of the predominant gut commensal bacteria in insects, its establishment in various niches within the gut has not been characterized well. In this study, Enterococcus mundtii was inoculated into the silkworm (Bombyx mori L.) to investigate its biological functions. Genome-based analysis revealed that its successful colonization is related to adherence genes (ebpA, ebpC, efaA, srtC, and scm). This bacterium did not alter the activities of related metabolic enzymes or the intestinal barrier function. However, significant changes in the gene expressions levels of Att2, CecA, and Lys suggest potential adaptive mechanisms of host immunity to symbiotic E. mundtii. Moreover, 16S metagenomics analysis revealed a significant increase in the relative abundance of E. mundtii in the intestines of silkworms following inoculation. The intestinal microbiome displayed marked heterogeneity, an elevated gut microbiome health index, a reduced microbial dysbiosis index, and low potential pathogenicity in the treatment group. Additionally, E. mundtii enhanced the breakdown of carbohydrates in host intestines. Overall, E. mundtii serves as a beneficial microbe for insects, promoting intestinal homeostasis by providing competitive advantage. This characteristic helps E. mundtii dominate complex microbial environments and remain prevalent across Lepidoptera, likely fostering long-term symbiosis between the both parties. The present study contributes to clarifying the niche of E. mundtii in the intestine of lepidopteran insects and further reveals its potential roles in their insect hosts.